The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
SiLent chains utilize links with inverted teeth for the transmission of power. Sets or rows of inverted tooth links are interleaved and connected by pins to form the chain assembly. Guide links are press fit on the pins and included along the outside of the link rows to maintain the chain on the sprockets. In the present invention, the chain construction eliminates the need for guide links. Instead of guide links, the chain uses inverted tooth links with differing crotch heights to both transmit power and maintain the chain on the sprockets. The different crotch heights provide a self-guiding function and avoid the need for conventional guide links.
The present invention has particular application to chain assemblies in which the sprockets are offset, or phased, to modify the impact noise spectrum and chordal action noise spectrum. In a phased chain system, a single chain assembly is replaced by two side-by-side chains that are phased or offset by one-half pitch. By eliminating the need for conventional guide links, the present invention permits a narrower chain for use in the phased chain system. The present invention also has particular application to engine timing systems where narrow chain systems are typically required.
As previously mentioned, silent chains are typically formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot members or pins, which are typically round pins or rocker joint pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
Conventional silent chains typically include both guide links and inverted tooth links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act only to position the chain laterally on the sprocket. Guide links do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and sprocket. Each inverted tooth link includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links, or driving links, contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the links and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft. A chain for an engine timing drive application is shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference. Various types of engine timing systems and configurations are also shown in U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993, which is incorporated herein by reference.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket at a particular moment or time increment.
Many efforts have been made to decrease the overall noise level and pitch frequency noise distribution in chain drives of the silent chain variety to minimize the objectionable effects of the pure sonic tones. Several of those efforts are discussed in the above-mentioned U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993. The present invention finds application along with some of the noise reduction concepts discussed in the above-mentioned application, including randomization and phasing of the chain assemblies. However, the present invention has broader applications to chain systems that include, for example, non-phased chains and sprockets or non-randomization of link profiles.
Phasing the chain and sprocket relationship can reduce the number of chain link teeth (or mass) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. The chain randomization and sprocket phasing modifications can result in a decrease in the overall noise level of the chain as well as pitch frequency noise level.
However, in the narrow chain assembly package requirements of modern engine timing systems, the use of a phased chain system can be difficult in that the single chain is often replaced by two chains that are used in side-by-side and phased relation. Modern engine timing systems often have as few as four links across the non-guide row and four or five links across the guide row. In order to package such a timing system in a phased system in approximately the same axial length, without decreasing the link thickness, the chain system requires the use of chains laced in a 2.times.2 lacing, i.e., two links across the guide row and two links across the non-guide row.
The use of two conventional (non-driving) guide links in the guide row results in the absence of a driving contact with the sprocket in every other row. Such a construction that fails to provide a driving or power transmission contact with the sprocket in every row can result in a noisier chain than a chain in which every row has a driving contact with the sprocket. The present invention is directed to overcoming such a disadvantage. In conjunction with the novel chain assembly, the present invention also provides a modified sprocket construction.